1. Field of the Invention
The present invention relates to a method of producing solid fatty microspheres (fine particles) for use in the food industry, the manufacturing of drugs and cosmetics, etc.
2. Description of Related Art
At present, natural oils and fats having a high melting point such as fish oils, animal fats or the like are dumped as waste oils. This is a serious loss from the standpoint of resource utilization and efficiency.
Therefore, it is considered that natural oils and fats having a high melting point such as fish oils, animal fats or the like can be utilized in the production of foods, drugs and cosmetics. However, in this case, it is necessary to adjust or modify the natural oils and fats having a high melting point to be dozens of xcexcm in the size thereof and to be in the form of uniform particles.
As a method of producing solid microspheres, there is already known a suspension polymerization method and an emulsion polymerization method.
In the suspension polymerization method, microspheres are composed by polymerizing a dispersed phase of emulsions. In the emulsion polymerization method, microspheres are composed by conducting a polymerization reaction in the micelle of a surfactant.
With the suspension polymerization method, it is difficult to obtain monodispersed microspheres because the distribution of particle diameter of produced microspheres depends on that of the emulsions.
With the emulsion polymerization method, the particle diameter of composed microspheres is usually about 0.1 xcexcm. If a seed emulsion polymerization method or a two-stage swelling method is used, microspheres the diameter of which is dozens of xcexcm can be obtained; however, it takes complicated processes involving high costs.
Furthermore, with the conventional methods, it is impossible to produce microspheres consistently and in large quantities.
According to the present invention, there is provided a method of consistently producing microspheres of natural oils and fats having a high melting point, such as hydrogenated fish oils, cattle fats or the like, the microspheres being dozens of xcexcm in size and having a small standard deviation (being uniform in size).
Specifically, according to the present invention, there is provided a method of producing microspheres, comprising the following steps:
heating oils and fats having a high melting point to a temperature above the melting point thereof to liquify same, holding oils and fats to be in a liquid state; and forming a dispersed phase of the liquid oils and fats;
pressurizing the dispersed phase and forming emulsions by dispersing said dispersed phase into a continuous phase via a plurality of microchannels having a predetermined width;
producing a suspension of solid microspheres by cooling and solidifying said emulsions; and
withdrawing the microspheres of oils and fats having a high melting point by removing said continuous phase from said suspension.
It is preferable to employ an apparatus which the applicant proposes in Japanese Laid-Open Patent Application No. 9-225291 as an apparatus for producing the above-mentioned emulsions.
In the apparatus proposed in Japanese Laid-Open Patent Application No. 9-225291, emulsions are produced by dispersing a liquid dispersed phase into a continuous phase at room temperature. Therefore, the apparatus can not be applied directly to the production of emulsions in which natural oils and fats having a high melting point are used as a dispersed phase; however, if a heating apparatus and a constant temperature apparatus for natural oils and fats having a high melting point are added, the apparatus can be applied to the implementation of the present invention.
In the above-mentioned apparatus, microchannels are formed, and via the microchannels a dispersed phase enters a continuous phase. In this case, it is preferable that a convex base is formed on a surface of another base, a plurality of walls are formed on a terrace which is an upper surface of the convex base, and spaces between the walls define microchannels.
In addition, it is preferable to add a surfactant, besides the oils and fats having a high melting point which become liquid, as the dispersed phase. By adding a surfactant, the interfacial tension decreases, and as a result of this, it is possible to decrease the pressure necessary to obtain break-through (i.e. minimum pressure at which the dispersed phase enters the continuous phase).
As mentioned above, it is necessary to apply a predetermined pressure to the dispersed phase to make the dispersed phase enter the continuous phase. It is preferable to set the pressure at 0.5 kPa or more and 1.3 kPa or below in a case where the terrace is positioned at a distance of 2-4 mm from an end of the base and the microchannels are 10-20 xcexcm in width and 5-10 xcexcm in depth. In the case where pressure is set below 0.5 kPa, it is hard to make the dispersed phase enter the continuous phase. On the other hand, in the case where pressure is over 1.3 kPa, it is hard to form microspheres because portions of the dispersed phase being dispered into the continous phase become connected.
As a means for withdrawing microspheres from emulsions in which the dispersed phase is dispersed within the continuos phase in of the form of microspheres, it is possible to freeze and dry, the suspension of solid microspheres to remove the continuous phase after leaving emulsions for a predetermined period of time at room temperature.